1. Field of the Invention
The present invention relates generally to apparatus for removing obstructive material from an occluded lumen of a patient, and more specifically to a catheter mounted electrode device disposable within an occluded stent implanted within a lumen and operative to cause an electrified current to flow through the stent and cause ablation of obstructive material formed in and around the stent.
2. Description of the Prior Art
Obstructive material may be formed in virtually all of the lumens in a body, and may be composed of many different substances. These obstructions may interfere with material transport and fluid flow within the lumen. One example of obstructive material formed within a lumen is atherosclerotic plaque formed within a coronary artery. Other obstructions may occur in any vein or artery such as a coronary, carotid, neurological, peripheral, or renal vein or artery. Additional types of lumens which may be obstructed include bile ducts, all lumens of the genital-urinary tract such as fallopian tubes, and lumens of the gastrointestinal tract such as the intestines or colon. Examples of obstructive material include: all forms of plaque such as fatty plaque, fibrous plaque, and calcific plaque; fibrotic material; mucous; thrombus; and blood clots. The above mentioned lumens and obstructive materials are given as examples only.
A variety of methods and devices have been developed to remove obstructive material from occluded lumens, or to at least alleviate the obstruction. Catheters equipped with cutting blades may be used to slice the obstruction from the lumen. Other methods use heat to resolve obstructive material. It is known that localized heating of a blood vessel wall may prevent the proliferation of smooth muscle cells which are believed to cause restenosis. Laser angioplasty devices generally supply energy to the tip of a catheter to cauterize or bum away obstructions.
Radio frequency (RF) ablation is also known in the prior art for ablating obstructive material formed within a lumen. RF current is directed from an RF power source to an ablating electrode, from which the RF current is provided to the obstructive material. In a monopolar RF ablation device, current return is typically provided via a conductive plate attached to the body of the patient and coupled to the power supply. In a multipolar RF ablation device, more than one electrode is provided at the distal end of the catheter, and the current flows through the obstructive material between at least two of these electrodes. An example of an RF catheter is described in Jannsen (U.S. Pat. No. 5,454,809).
Balloon angioplasty is another common method of removing obstructive material from an occluded lumen. In accordance with balloon angioplasty techniques, a catheter having a deflated balloon is introduced into an occluded lumen and the balloon is inflated. The inflated balloon applies pressure to the obstruction, and to the wall of the lumen. The balloon stretches the lumen, so that fluid flow through the lumen may be improved. However, balloon angioplasty tends to stretch the elastic artery beyond its ability to recoil causing the lumen to contract after the balloon is deflated and withdrawn from the lumen. A well known solution to the problem of lumen contraction is to insert a stent into the lumen.
A stent typically comprises an expandable coil spring or wire-mesh tube. In accordance with a common method for implanting a stent within an occluded lumen, the stent is mounted upon an inflatable balloon catheter. The catheter assembly is then delivered to the occluded area, and the balloon is inflated to radially force the stent into contact with the occlusion. As the stent expands, the lumen of the blood vessel is opened and blood flow is restored. After complete expansion of the stent, the balloon catheter is deflated and removed, leaving the stent behind to buttress and prevent elastic recoil of the blood vessel wall.
While stents have proven effective in preventing lumen restriction, complications often may arise in their use. In particular, obstructions may build up in or through the stent in much the same manner as they would if the stent was not in place, such as by, for example, tissue growth. The stent may irritate the tissue and may allow for thrombin, plaque, or other substances to accumulate on the interior surface of the stent, and on the outer surface of the stent between the stent and the lumen. Such accumulation, referred to as restenosis, may again restrict fluid flow through the lumen, so that efficacy of the stent is reduced or, in severe cases, eliminated. Stent restenosis affects approximately 20% of all stents placed in the coronary vasculature. The problem of restenosis is commonly addressed by attempting to dilate the lumen of the vessel with conventional balloon angioplasty, or by the use of various atherectomy devices. Stent manufacturers have tried to address the problem of restenosis using antifibrogenic coatings, and in some instances with the use of radioactive materials contained within the stent.
Another method for removing obstructive material from within a stent is RF ablation. However, the presence of a stent in an occluded lumen causes some complications for RF ablation because stents are typically formed of conductive material. If an ablating electrode comes into contact with the stent, a short circuit could occur, which may damage the ablation catheter, the stent, or the lumen.
Jannsen (U.S. Pat. No. 5,749,914, filed May 28, 1996, and issued May 12, 1998) discloses an electrosurgical device for ablation of obstructive material within a stent. The device includes a catheter, or elongate flexible tube, having a distal end and a proximal end. One or more ablation electrodes are positioned at the distal end of the catheter, and a power supply is provided in electrical communication with the electrodes. The electrodes are shielded from direct contact with the stent in order to prevent a possible short circuit that may occur if the electrode contacts the stent. The catheter is inserted into the stent, and a first ablation electrode disposed proximate the distal end of the catheter is shielded from physical contact with the stent by a lip of the catheter wall.
Jannsen describes a plurality of circumferentially divided electrodes seated in an annular ridge formed in the exterior wall of the catheter, the electrodes being sized so that they are recessed within the annular ridge. Jannsen also discloses a plurality of ring electrodes disposed along the longitudinal axis of the catheter. A plurality of spacers, projecting radially away from the catheter axis, are disposed between adjacent ones of the ring electrodes. The spacers have a diameter greater than the diameter of the ring electrodes so that the electrodes are prevented from contacting the stent.
According to Jannsen, the stent may conduct current and act as a virtual ground shielding all tissue located exterior to the stent. Jannsen further discloses directly grounding a stent via conducting stylets or probes extending radially from the catheter in order to improve the shielding effect of the stent. A return electrode is provided in electrical communication with the current supply, the return electrode being attachable to a patient. Jannsen discloses a return electrode sized so that it will contact the stent, thereby grounding the stent. This lowers the impedance between the return electrode and the ablating electrodes, and allows for precise ablating of obstructive material between the electrodes and the stent.
As described in Jannsen, it may be inconvenient to have the electrode sized to contact the stent, because the electrode may then interfere with the longitudinal motion of the catheter through the stent. One solution to this problem, as described by Jannsen, is to use an, inflatable balloon located beneath the electrode to selectively increase the diameter of the catheter at the position of the electrode to bring the electrode into contact with the stent. The balloon may be deflated when the catheter is moved through the lumen, and may be inflated when the catheter is in an appropriate position. However, a problem with this method is that using a balloon to extend an electrode radially outward is expensive and awkward. Also, the contact area between the electrode and obstructive material is limited by the shape of electrodes disposed on the balloon. Moreover, the area of contact between the electrode and obstructive material, and ultimately between the electrode and stent, is difficult to optimize using an electrode disposed on an inflatable balloon.
What is needed is a catheter mounted electrode assembly for insertion into a stent to create localized current flow to and through the stent to cause ablation of obstructive material formed within and around the stent.
What is also needed is a multipolar electrode catheter assembly for ablation of obstructive material formed within and around a stent wherein the electrodes are shaped to provide an optimal area of contact between the obstructive material and the electrodes, and ultimately between the electrodes and the stent after obstructive material has been ablated.
Further needed is an electrode catheter assembly for ablation of obstructive material formed within and around a stent wherein the electrodes are shaped so as to precisely control the flow of current between the electrodes and through the obstructive material and the stent in order to maximize efficiency in ablating the obstructive material.
It is therefore an object of the present invention to provide a catheter assembly having means for creating an electrical current flow through a metallic stent disposed within a lumen to cause ablation of obstructive material formed within and around the stent.
It is also an object of the present invention to provide an electrode catheter assembly for ablation of obstructive material formed within and around a stent wherein the electrodes are shaped to provide an optimal area of contact with the obstructive material and the electrodes, and ultimately between the electrodes and the stent after obstructive material has been ablated.
It is a further object of the present invention to provide an electrode catheter assembly for ablation of obstructive material formed within and around a stent wherein the electrodes are shaped so as to precisely control the flow of current between the electrodes, through the obstructive material, and through the stent in order to maximize efficiency in ablating the obstructive material.
Briefly, a presently preferred embodiment of the present invention includes a catheter assembly for ablation of obstructive material formed within and around a stent inserted within a lumen. The catheter assembly includes an elongate flexible tube having a distal end and a proximal end, and an electrode assembly attached to the distal end of the tube. The electrode assembly includes: a first electrode formed by a substantially cylindrical body defining a longitudinal axis and having a first end, and an opposite second end, the body having a plurality of slits formed therein, each of the slits extending substantially parallel to the axis from a corresponding first point proximate the first end to a corresponding second point proximate the second end, the slits defining a plurality of elongated deformable segments of the body; and a second electrode disposed along the axis at a distance from the first electrode. A spacer means, disposed between the first and second electrodes, is operative to physically separate and electrically insulate the first electrode from the second electrode.
Electrical transmission means is passed through the tube to provide: a first electrical path between a power supply and the first electrode; and a second electrical path between the second electrode and the power supply. Actuator means is provided for moving the first end of the cylindrical body toward the second end of the body causing the segments to be deformed so that portions thereof are extended radially away from the axis, whereby when the catheter assembly is inserted into a lumen and positioned within an occluded stent, the deformable segments establish an electrically conductive path to the stent.
Each of the deformable segments has a corresponding weakened portion formed along a line transverse to the longitudinal axis of the cylindrical body, the segments being deformable about the corresponding weakened portions. The weakened portions of the segments may be formed by perforating, crimping, or bending the segments along the transverse lines.
In an embodiment, the second electrode is also formed by a substantially cylindrical body defining a longitudinal axis and having a first end, and an opposite second end, the body having a plurality of slits formed therein, each of the slits extending substantially parallel to the axis from a corresponding first point proximate the first end to a corresponding second point proximate the second end, the slits defining a plurality of elongated deformable segments of the body.
The actuator means preferably includes: a cable passing through the tube and having a distal end connected to the second end of the cylindrical body, and a proximal end; and retracting means connected to the proximal end of the cable and operative to retract the cable causing the second end to be moved toward the first end of the body.
An important advantage of the present invention is that the deformable segments of the electrodes, which extend radially away from the axis, provide a large surface area for contacting obstructive material formed within a stent implanted within a lumen, thereby allowing for current to be conducted through a large amount of the obstructive material providing efficient ablation of the material. Also, as the obstructive material is ablated by energy provided via the electrodes, the segments of the electrodes may be further extended radially toward the inner wall of the stent, ultimately contacting the inner wall of the stent.
The foregoing and other objects, features, and advantages of the present invention will be apparent from the following detailed description of the preferred embodiment which makes reference to the several figures of the drawing.